During the second continuation year of this project, it is proposed to refine further the correlation between biochemical findings and morphological observations based on transmission electron microscopy, on the general subject of glycogen metabolism in human skin fibroblasts grown in tissue culture. The aim of this long-range study is to gather information on the autophagy of glycogen in such cells, to measure quantitatively the rate of this process, and to compare it with the rate of glycogen hydrolysis within lysosomes. Normal control cells and cells from patients with various types of glycogen storage disease will be used. Studies will continue on the enzymatic mechanism by which fibroblasts from patients who lack the normal "glycogen branching enzyme" (that is, from patients with Type IV Glycogen Storage Disease) nevertheless are able to synthesize a glycogen-like polysaccharide which contains some branch points.